From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755855AbbAWPxp (ORCPT ); Fri, 23 Jan 2015 10:53:45 -0500 Received: from relay.parallels.com ([195.214.232.42]:48729 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751765AbbAWPxn (ORCPT ); Fri, 23 Jan 2015 10:53:43 -0500 Message-ID: <1422028412.6345.6.camel@tkhai> Subject: [RFC] sched, x86: Prevent resched interrupts if task in kernel mode and !CONFIG_PREEMPT From: Kirill Tkhai To: CC: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Date: Fri, 23 Jan 2015 18:53:32 +0300 Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's useless to send reschedule interrupts in such situations. The earliest point, where schedule() call is possible, is sysret_careful(). But in that function we directly test TIF_NEED_RESCHED. So it's possible to get rid of that type of interrupts. How about this idea? Is set_bit() cheap on x86 machines? --- arch/x86/kernel/entry_64.S | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index c653dc4..a046ba8 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -409,6 +409,13 @@ GLOBAL(system_call_after_swapgs) movq_cfi rax,(ORIG_RAX-ARGOFFSET) movq %rcx,RIP-ARGOFFSET(%rsp) CFI_REL_OFFSET rip,RIP-ARGOFFSET +#if !defined(CONFIG_PREEMPT) || !defined(SMP) + /* + * Tell resched_curr() do not send useless interrupts to us. + * Kernel isn't preemptible till sysret_careful() anyway. + */ + LOCK ; bts $TIF_POLLING_NRFLAG,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) +#endif testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) jnz tracesys system_call_fastpath: @@ -427,6 +434,9 @@ GLOBAL(system_call_after_swapgs) * Has incomplete stack frame and undefined top of stack. */ ret_from_sys_call: +#if !defined(CONFIG_PREEMPT) || !defined(SMP) + LOCK ; btr $TIF_POLLING_NRFLAG,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) +#endif movl $_TIF_ALLWORK_MASK,%edi /* edi: flagmask */ sysret_check: